simple present passive?

one of the coursebooks I use teaches present simple passive by describing the origins of products. I don't think "This watch is made of real gold" is a passive sentence. If it is, what is the active form?? As far as I know "is" in the sentence above is stative and so have no passive form.
Or Am I wrong???

Yes, it is a passive - present simple passive of the verb make. The passive is formed with BE (auxiliary) + past participle main verb - so here : is made.

The active form would be (for example) Rolex makes watches out of real gold. "Rolex" (or whoever) is not mentioned in the passive sentence because one of the uses of the passive is to allow us to keep the subject-verb structure of English even if there is no "doer" (or cause) of the action, or if we want to focus not on the "doer" but (as here) on what is done.

As another example consider : They make paper in Finland. Grammatically it's fine and in conversation would be normal. But in a more formal context (eg a presentation on the economy of Scandinavia) the "empty" subject (who are "they" ?) would be out of place. So the passive would normally be chosen - Paper is made in Finland.

Your confusion is probably due to the fact that we often think of what are really passive verbs (BE + Past Participle) as if the past participle is an adjective - and in fact it does have an adjectival function. So for example, if you say I'm tired, David was annoyed or I'm not interested, there's actually an underlying idea that can be expressed by an active verb :Shopping tires me / The children's behaviour annoyed David / Your proposal doesn't interest me.

In this situation the choice of the passive would probably be because the cause of the action is obvious from the context (which may be situational or in the previous discourse.) :

- How did David react to the children's behaviour?
- He was annoyed.

- What do you think of my proposal?
- I'm not interested.

If we chose to use the active we'd reduce the subject to a pronoun It annoyed him / It doesn't interest me because it's redundant in the context. Using the passive allows us to exclude it all together.